White silicon nitride ceramic, method for producing the same, and use thereof

Abstract

The application provides white silicon nitride ceramics and a preparation method and application thereof. The method comprises the following steps: providing raw materials, wherein the raw materials comprise silicon nitride powder, a sintering aid, rare earth oxides and a dispersing agent, the rare earth oxides comprise at least one of lanthanum oxide, gadolinium oxide and lutetium oxide; mixing the raw materials, then performing ball milling, and then performing drying to obtain to-be-sintered materials; performing compression molding on the to-be-sintered materials to obtain to-be-sintered green bodies; sintering the to-be-sintered green bodies, and obtaining white silicon nitride ceramics after cooling. In this way, the to-be-sintered materials are sintered by using the above components, and the mixed system of the sintering aid and the rare earth oxides in the raw materials can reduce the concentration of free silicon inclusions in the ceramics, reduce the formation of color centers, introduce appropriate pores in the ceramics, and thus improve the light reflection ability of the ceramics, and further improve the whiteness of the silicon nitride ceramics. Therefore, the white silicon nitride ceramics with high strength and good comprehensive performance can be prepared by using the above method.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, specifically relating to a white silicon nitride ceramic, its preparation method, and its application. Background Technology

[0002] Silicon nitride ceramics possess excellent mechanical properties, promote bone growth, and have antibacterial effects, making them widely used in bone implant materials and other fields. However, during the sintering process, free silicon often precipitates in the grain boundary phase, acting as color centers and causing the ceramic to darken in color. Furthermore, during high-temperature sintering processes such as hot pressing, silicon nitride ceramics frequently come into contact with carbon (C), which inevitably penetrates the ceramic, further deepening its color. The dark color of silicon nitride ceramics severely limits their application in fields with high aesthetic requirements, such as dental materials. Therefore, white porous silicon nitride ceramics are often prepared by introducing pores to meet these requirements. However, porous silicon nitride ceramics have low strength, often only a fraction of that of human bone, resulting in poor reliability. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a white silicon nitride ceramic, its preparation method, and its application. This method produces a white silicon nitride ceramic with high strength.

[0004] In a first aspect, the present invention provides a method for preparing white silicon nitride ceramics. According to an embodiment of the present invention, the method includes: (1) providing raw materials, the raw materials including silicon nitride powder, sintering aid, rare earth oxides and dispersant, the rare earth oxides including at least one of lanthanum oxide, gadolinium oxide and lutetium oxide; (2) mixing the raw materials and then ball milling them, and then drying them to obtain a material to be sintered; (3) pressing the material to be sintered into a blank to be sintered; (4) sintering the blank to be sintered and cooling it to obtain the white silicon nitride ceramic.

[0005] According to embodiments of the present invention, the preparation method of the present invention uses the above-mentioned raw materials for sintering. On the one hand, during the sintering process, the free silicon precipitated in the grain boundary phase of silicon nitride ceramics is more easily dissolved in the liquid phase formed by rare earth oxides and further forms silicon compounds, thereby reducing the concentration of free silicon inclusions generated during the sintering process and reducing the formation of color centers. On the other hand, compared with the traditional silicon nitride sintering aid system, the mixed system of sintering aid and rare earth oxides used in the present invention has a higher viscosity in the liquid phase formed during the sintering process, and the gas is less likely to move in the liquid phase and is difficult to be discharged from the silicon nitride ceramic. The gas is more likely to remain inside the silicon nitride ceramic and form pores. By introducing appropriate pores into the silicon nitride ceramic, the light reflection ability of the silicon nitride ceramic can be improved, thereby further improving the whiteness of the silicon nitride ceramic. Therefore, white silicon nitride ceramics can be prepared by the above method of the present invention. Furthermore, the mixed system of sintering aid and rare earth oxides of the present invention does not introduce excessive pores into the silicon nitride ceramics during the sintering process, thus not affecting the strength of the silicon nitride ceramics. As a result, the prepared white silicon nitride ceramics have high strength and good application value.

[0006] In addition, the preparation method according to the above embodiments of the present invention may also have the following additional technical features:

[0007] According to an embodiment of the present invention, the mass ratio of the sintering aid to the rare earth oxide is 1:(1-9). This effectively reduces the concentration of free silicon during sintering, thereby reducing the concentration of color centers in the silicon nitride ceramic and facilitating the production of white silicon nitride ceramic.

[0008] According to an embodiment of the present invention, in the raw materials, the silicon nitride powder comprises 70-95 parts by weight, the sum of the sintering aid and the rare earth oxide comprises 5-30 parts by weight, and the dispersant comprises 100-300 parts by weight. Thus, white silicon nitride ceramics with high strength and good performance can be prepared.

[0009] According to embodiments of the present invention, the sintering aid includes at least one of alumina and magnesium oxide. Thus, white silicon nitride ceramics with superior mechanical properties can be prepared.

[0010] According to an embodiment of the present invention, the dispersant includes at least one of anhydrous ethanol, anhydrous methanol, anhydrous acetone, and deionized water.

[0011] According to an embodiment of the present invention, in step (4), the green blank to be sintered is embedded with powder before sintering, and the powder used for embedding includes at least one of boron nitride powder and silicon nitride powder. Thus, by embedding powder during sintering, the formation of free silicon during cooling can be reduced, thereby reducing the formation of color centers in silicon nitride ceramics and further improving the whiteness of silicon nitride ceramics.

[0012] According to an embodiment of the present invention, in step (4), the sintering is performed by gas pressure sintering, with a sintering pressure of 0.1 MPa-20 MPa, a sintering temperature of 1700℃-2000℃, and a holding time of 0.5h-12h. This avoids carbon penetrating into the silicon nitride ceramic during sintering, thus facilitating the preparation of white silicon nitride ceramic.

[0013] According to an embodiment of the present invention, in step (4), the cooling rate is 0.5℃ / min-20℃ / min. This further reduces the concentration of free silicon in the silicon nitride ceramic and improves its whiteness.

[0014] According to an embodiment of the present invention, the porosity of the white silicon nitride ceramic is 0.2%-5%. This improves the reflectivity of the silicon nitride ceramic, thereby further enhancing its whiteness.

[0015] According to an embodiment of the present invention, in step (2), the ball-to-material mass ratio of the ball mill is (3-4):1, the rotation speed is 200 r / min-400 r / min, and the milling time is 1 h-24 h. This allows the silicon nitride powder, sintering aid, and rare earth oxides to be fully and uniformly mixed, which is beneficial for obtaining white silicon nitride ceramics with good mechanical properties through sintering.

[0016] According to an embodiment of the present invention, in step (2), the drying temperature is 50℃-80℃ and the drying time is 8h-24h.

[0017] According to an embodiment of the present invention, in step (2), the material to be burned is sieved, and the mesh size of the sieve is 50-200 mesh.

[0018] According to an embodiment of the present invention, in step (3), the pressing and molding includes: dry pressing the material to be fired to obtain a green body, wherein the dry pressing pressure is 0.1 MPa-10 MPa and the time is 0.5 min-10 min; then the green body is subjected to cold isostatic pressing treatment, wherein the cold isostatic pressing pressure is 100 MPa-300 MPa and the time is 0.5 min-10 min, to obtain a green body to be fired. Thus, the prepared white silicon nitride ceramic has high strength and good overall performance.

[0019] In a second aspect, the present invention provides a white silicon nitride ceramic. According to an embodiment of the present invention, the white silicon nitride ceramic is prepared by the method described above. Therefore, the white silicon nitride ceramic has high strength and good application value.

[0020] In a third aspect, the present invention provides the application of the white silicon nitride ceramic in the medical field. The white silicon nitride ceramic prepared by the method of the present invention has high strength and can be applied in the field of bone implant materials; furthermore, its white appearance makes it suitable for applications in dental materials and other fields where aesthetics are critical.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0023] Figure 1 This is a flowchart of a method for preparing white silicon nitride ceramics in one embodiment of the present invention.

[0024] Figure 2 The graph shows the reflectance of the white silicon nitride ceramic prepared in Example 1 of this invention and the color of the silicon nitride ceramic sample.

[0025] Figure 3 The graph shows the light reflectance curve of the white silicon nitride ceramic prepared in Example 2 of this invention and the color of the silicon nitride ceramic sample.

[0026] Figure 4 The graph shows the light reflectance curve of the white silicon nitride ceramic prepared in Example 3 of this invention and the color of the silicon nitride ceramic sample.

[0027] Figure 5 The graph shows the reflectance curve of the silicon nitride ceramic prepared in Comparative Example 1 of this invention and the color of the silicon nitride ceramic sample. Detailed Implementation

[0028] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0029] In a first aspect, the present invention provides a method for preparing white silicon nitride ceramics. According to an embodiment of the present invention, referring to... Figure 1 The method includes the following steps:

[0030] S100: Provide raw materials

[0031] In this step, the raw materials include silicon nitride powder, sintering aid, rare earth oxides and dispersants, wherein the rare earth oxides include at least one of lanthanum oxide, gadolinium oxide and lutetium oxide.

[0032] During the sintering process, rare earth oxides in the raw materials form a liquid phase at high temperatures. Free silicon precipitated from the grain boundary phase of silicon nitride ceramics can dissolve well in the liquid phase formed by rare earth oxides and further form silicon compounds. This effectively reduces the concentration of free silicon inclusions generated during sintering, thereby reducing the formation of color centers in silicon nitride ceramics and promoting their white color. On the other hand, compared with the traditional silicon nitride sintering aid system, the mixed system of sintering aid and rare earth oxides used in this invention has a higher viscosity in the liquid phase formed during sintering. Gases are less mobile in the liquid phase and are difficult to escape from the silicon nitride ceramics. Gases are more likely to remain inside the silicon nitride ceramics, forming pores. By introducing appropriate pores into the silicon nitride ceramics, the light reflectivity of the silicon nitride ceramics can be improved, thereby further improving the whiteness of the silicon nitride ceramics. Furthermore, the mixed system of sintering aid and rare earth oxides in this invention does not introduce excessive pores into the silicon nitride ceramics during sintering, thus not affecting the strength of the silicon nitride ceramics. Furthermore, rare earth oxides can also act as sintering aids, and when combined with sintering aids in the raw materials, they can effectively improve the mechanical properties of silicon nitride ceramics. As an example, in this invention, the sintering aids may include at least one of alumina and magnesium oxide.

[0033] In some embodiments of the present invention, the mass ratio of sintering aid to rare earth oxides can be 1:(1-9), such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, etc. By using the above-mentioned mass ratios of sintering aid and rare earth oxides, and appropriately increasing the relative amount of rare earth oxides, the concentration of free silicon during sintering can be reduced more effectively, thereby reducing the concentration of color centers in silicon nitride ceramics. This is beneficial for preparing white silicon nitride ceramics.

[0034] In some embodiments of the present invention, the weight parts of silicon nitride powder in the above-mentioned raw materials can be 70-95 (e.g., 70, 72, 75, 78, 80, 83, 85, 87, 90, 93, 95, etc.), the sum of the weight parts of sintering aids and rare earth oxides can be 5-30 (e.g., 5, 7, 10, 12, 15, 17, 20, 23, 25, 27, 30, etc.), and the weight parts of dispersant can be 100-300 (e.g., 100, 130, 160, 180, 200, 220, 250, 270, 300, etc.). Using raw materials with the above-mentioned components is more conducive to preparing white silicon nitride ceramics with higher strength and better performance. As an example, in the present invention, the dispersant may include at least one of anhydrous ethanol, anhydrous methanol, anhydrous acetone, and deionized water.

[0035] S200: The raw materials are mixed and then ball-milled, followed by drying.

[0036] In this step, the components of the raw materials are first mixed to obtain a silicon nitride slurry, which is then added to a ball mill jar for ball milling. Ball milling allows the silicon nitride powder, sintering aids, and rare earth oxides to be fully and uniformly mixed and further refined, thereby achieving a better sintering effect. In some embodiments of the present invention, the ball-to-material mass ratio in the ball mill can be (3-4):1 (e.g., 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, etc.), the rotation speed can be 200 r / min-400 r / min (e.g., 200 r / min, 240 r / min, 280 r / min, 300 r / min, 340 r / min, 380 r / min, 400 r / min, etc.), and the milling time can be 1 h-24 h (e.g., 1 h, 3 h, 5 h, 7 h, 10 h, 13 h, 15 h, 17 h, 20 h, 22 h, 24 h, etc.). Under the above milling conditions, the silicon nitride powder, sintering aid, and rare earth oxides can be thoroughly and uniformly mixed, which is beneficial for obtaining white silicon nitride ceramics with good mechanical properties through sintering. Furthermore, the grinding balls used in the ball mill are preferably made of silicon nitride material, thus avoiding the introduction of impurities.

[0037] The ball milling material obtained is then placed in a drying oven for drying. The drying temperature can be 50℃-80℃ (e.g., 50℃, 54℃, 58℃, 62℃, 66℃, 70℃, 74℃, 78℃, 80℃, etc.), and the drying time can be 8h-24h (e.g., 8h, 10h, 14h, 18h, 20h, 22h, 24h, etc.).

[0038] In some embodiments of the present invention, in order to obtain a more uniform powder, the dried material to be burned can be sieved, and the sieve mesh size is 50-200 mesh.

[0039] S300: Press the material to be burned obtained in step S200 into shape.

[0040] In this step, the material to be fired can first be added to the mold and dry-pressed to obtain a blank. The pressure of dry pressing can be 0.1MPa-10MPa (e.g., 0.1MPa, 1MPa, 2MPa, 4MPa, 6MPa, 8MPa, 10MPa, etc.), and the time can be 0.5min-10min (e.g., 0.5min, 1min, 2min, 4min, 6min, 8min, 10min, etc.). Then, the pressed blank is further compressed and densified using a cold isostatic press. The pressure of cold isostatic pressing can be 100MPa-300MPa (e.g., 100MPa, 150MPa, 200MPa, 250MPa, 300MPa, etc.), and the time can be 0.5min-10min (e.g., 0.5min, 1min, 2min, 4min, 6min, 8min, 10min, etc.). After the above pressing process, the green blank to be fired is obtained. By using the above-mentioned pressing and molding conditions, the density of silicon nitride ceramics can be improved, which is beneficial to preparing white silicon nitride ceramics with high strength and good overall performance.

[0041] S400: Sinter the green blank obtained in step S300.

[0042] In this step, sintering can be carried out using atmospheric pressure sintering, gas pressure sintering, or reaction sintering methods. After sintering, cooling yields white silicon nitride ceramics. Using atmospheric pressure sintering, gas pressure sintering, or reaction sintering methods can prevent carbon from penetrating into the silicon nitride ceramic during the sintering process, thus facilitating the preparation of white silicon nitride ceramics.

[0043] For example, in some embodiments of the present invention, gas pressure sintering is preferably used for sintering. The sintering pressure of gas pressure sintering can be 0.1MPa-20MPa (e.g., 0.1MPa, 1MPa, 2MPa, 4MPa, 6MPa, 8MPa, 10MPa, 12MPa, 14MPa, 16MPa, 18MPa, 20MPa, etc.), the sintering temperature can be 1700℃-2000℃ (e.g., 1700℃, 1750℃, 1800℃, 1850℃, 1900℃, 1950℃, 2000℃, etc.), and the holding time can be 0.5h-12h (e.g., 0.5h, 1h, 2h, 4h, 6h, 8h, 10h, 11h, 12h, etc.). During gas pressure sintering of silicon nitride ceramics, higher gas pressure generally leads to faster densification and lower porosity. This invention employs the aforementioned sintering conditions, and by controlling a suitable gas pressure, a certain amount of porosity can be retained within the silicon nitride ceramic. These porosity enhances the reflectivity of the silicon nitride ceramic; therefore, retaining appropriate porosity can further improve the whiteness of the silicon nitride ceramic. Simultaneously, a small amount of porosity does not affect the strength of the silicon nitride ceramic. For example, in some embodiments of this invention, the porosity of the prepared white silicon nitride ceramic can be 0.2%-5% (e.g., 0.2%, 0.4%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 4.8%, 5%, etc.). By controlling the porosity of silicon nitride ceramics within the aforementioned range, the reflectivity of silicon nitride ceramics can be improved, thereby further enhancing the whiteness of silicon nitride ceramics and ensuring that silicon nitride ceramics have high strength and better mechanical properties.

[0044] In some embodiments of the present invention, the green body to be sintered can be pre-embedded with powder before sintering. Pre-embedded powder sintering promotes the removal of SiO generated during sintering from the silicon nitride ceramic. SiO forms free silicon during subsequent cooling; pre-embedded powder promotes SiO removal, reducing the formation of free silicon during cooling, thereby lowering the concentration of color centers in the silicon nitride ceramic. As an example, the powder used for pre-embedded powder may include at least one of boron nitride powder and silicon nitride powder. Using the above-mentioned powder is more conducive to promoting the removal of SiO generated during sintering from the silicon nitride ceramic, thereby reducing the generation of free silicon during cooling and improving the whiteness of the silicon nitride ceramic.

[0045] In some embodiments of the present invention, the atmosphere during the sintering process can be nitrogen. Sintering under a nitrogen atmosphere can suppress the decomposition of silicon nitride, thereby helping to reduce the concentration of free silicon in silicon nitride ceramics.

[0046] In some embodiments of the present invention, during the cooling process, the cooling rate can be controlled within the range of 0.5℃ / min to 20℃ / min. For example, the cooling rate can be 0.5℃ / min, 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min, 19℃ / min, 20℃ / min, etc. During the cooling process, the SiO formed during the sintering of silicon nitride ceramics will react to produce free silicon. Controlling the cooling rate within the above range is beneficial for the residual N2 in the pores generated during the sintering process to react with Si, thereby reducing the concentration of free silicon inclusions in the silicon nitride ceramics, reducing the concentration of color centers, and improving the whiteness of the silicon nitride ceramics.

[0047] Therefore, according to embodiments of the present invention, white silicon nitride ceramics can be prepared using the above-described method of the present invention, and this method does not introduce excessive pores into the silicon nitride ceramics. Thus, the prepared silicon nitride ceramics have high strength and good application value.

[0048] In a second aspect, the present invention provides a white silicon nitride ceramic. According to an embodiment of the present invention, the white silicon nitride ceramic is prepared by the method described above. Therefore, the white silicon nitride ceramic has high strength and good application value.

[0049] In a third aspect, the present invention provides the application of the white silicon nitride ceramic in the medical field. The white silicon nitride ceramic prepared by the method of the present invention has high strength and can be applied in the field of bone implant materials; furthermore, its white appearance makes it suitable for applications in dental materials and other fields where aesthetics are critical.

[0050] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0051] Example 1

[0052] (1) Weigh out 90 parts of silicon nitride powder, 2 parts of magnesium oxide, 8 parts of lanthanum oxide and 150 parts of anhydrous ethanol according to the weight, and set aside.

[0053] (2) Add silicon nitride powder, magnesium oxide and lanthanum oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0054] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0055] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1 MPa for 2 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 10 min to obtain a raw blank to be fired.

[0056] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 5 MPa, the sintering temperature is 1800℃, the holding time is 10h, and then it is cooled with the furnace to obtain white silicon nitride ceramic.

[0057] The silicon nitride ceramic prepared in Example 1 is white in color, has a porosity of 1%, and a density of 3.29 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 13 GPa, and the fracture toughness is 6.9 MPa·m. 1 / 2 . Figure 2 The graph shows the reflectance of the silicon nitride ceramic prepared in Example 1 and the color of the silicon nitride ceramic sample.

[0058] Example 2

[0059] (1) Weigh out 90 parts of silicon nitride powder, 2 parts of magnesium oxide, 8 parts of gadolinium oxide and 150 parts of anhydrous ethanol according to the weight, and set aside;

[0060] (2) Add silicon nitride powder, magnesium oxide and gadolinium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0061] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0062] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0063] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 4 MPa, the sintering temperature is 1800℃, the holding time is 8h, and then it is cooled with the furnace to obtain white silicon nitride ceramic.

[0064] The silicon nitride ceramic prepared in Example 2 is white in color, has a porosity of 2%, and a density of 3.29 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 13.1 GPa, and the fracture toughness is 6.7 MPa·m. 1 / 2 . Figure 3 The graph shows the reflectance of the silicon nitride ceramic prepared in Example 2 and the color of the silicon nitride ceramic sample.

[0065] Example 3

[0066] (1) Weigh out 90 parts of silicon nitride powder, 2 parts of magnesium oxide, 8 parts of lutetium oxide and 150 parts of anhydrous ethanol according to the weight, and set aside for later use;

[0067] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0068] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0069] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0070] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 4 MPa, the sintering temperature is 1800℃, the holding time is 8h, and then it is cooled with the furnace to obtain white silicon nitride ceramic.

[0071] The silicon nitride ceramic prepared in Example 3 was white in color, had a porosity of 3%, and a density of 3.28 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 12.2 GPa, and the fracture toughness is 6.3 MPa·m. 1 / 2 . Figure 4 The graph shows the reflectance of the silicon nitride ceramic prepared in Example 3 and the color of the silicon nitride ceramic sample.

[0072] Example 4

[0073] (1) Weigh out 70 parts of silicon nitride powder, 15 parts of magnesium oxide, 15 parts of lanthanum oxide and 100 parts of anhydrous ethanol according to the weight parts, and set aside.

[0074] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0075] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0076] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0077] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 0.1 MPa, the sintering temperature is 1700℃, the holding time is 12h, and then it is cooled at a cooling rate of 20℃ / min to prepare white silicon nitride ceramic.

[0078] The silicon nitride ceramic prepared in Example 4 was white in color, had a porosity of 5%, and a density of 3.31 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 10.1 GPa, and the fracture toughness is 5.4 MPa·m. 1 / 2 .

[0079] Example 5

[0080] (1) Weigh out 95 parts of silicon nitride powder, 2.5 parts of magnesium oxide, 2.5 parts of lanthanum oxide and 300 parts of anhydrous ethanol according to the weight, and set aside for later use;

[0081] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0082] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0083] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0084] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 20 MPa, the sintering temperature is 2000℃, the holding time is 12 h, and then it is cooled at a cooling rate of 0.5℃ / min to prepare white silicon nitride ceramic.

[0085] The silicon nitride ceramic prepared in Example 5 was white in color, had a porosity of 0.2%, and a density of 3.24 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 15.4 GPa, and the fracture toughness is 6.8 MPa·m. 1 / 2 .

[0086] Example 6

[0087] (1) Weigh out 90 parts of silicon nitride powder, 4 parts of magnesium oxide, 3 parts of lanthanum oxide, 3 parts of gadolinium oxide and 200 parts of anhydrous ethanol according to the weight, and set aside;

[0088] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0089] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0090] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0091] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 10 MPa, the sintering temperature is 1900℃, the holding time is 0.5 h, and then the blank is cooled at a cooling rate of 10℃ / min to prepare white silicon nitride ceramic.

[0092] The silicon nitride ceramic prepared in Example 6 was white in color, had a porosity of 2%, and a density of 3.32 g / cm³. 3The phase composition is β-silicon nitride, the hardness is 13.2 GPa, and the fracture toughness is 7.2 MPa·m. 1 / 2 .

[0093] Example 7

[0094] (1) Weigh out 90 parts of silicon nitride powder, 4 parts of magnesium oxide, 3 parts of gadolinium oxide, 3 parts of lutetium oxide and 150 parts of anhydrous ethanol according to the weight parts, and set aside for later use;

[0095] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0096] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0097] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0098] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 10 MPa, the sintering temperature is 1900℃, the holding time is 12h, and then it is cooled at a cooling rate of 10℃ / min to prepare white silicon nitride ceramic.

[0099] The silicon nitride ceramic prepared in Example 7 was white in color, had a porosity of 0.5%, and a density of 3.36 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 15.5 GPa, and the fracture toughness is 7.2 MPa·m. 1 / 2 .

[0100] Example 8

[0101] (1) Weigh out 95 parts of silicon nitride powder, 0.5 parts of magnesium oxide, 2.25 parts of lanthanum oxide, 2.25 parts of lutetium oxide and 150 parts of anhydrous ethanol according to the weight ratio, and set aside for later use;

[0102] (2) Add silicon nitride powder, magnesium oxide and lutetium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0103] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0104] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0105] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 20 MPa, the sintering temperature is 2000℃, the holding time is 6h, and then it is cooled at a cooling rate of 15℃ / min to prepare white silicon nitride ceramic.

[0106] The silicon nitride ceramic prepared in Example 8 was white in color, had a porosity of 4%, and a density of 3.28 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 12.1 GPa, and the fracture toughness is 5.8 MPa·m. 1 / 2 .

[0107] Comparative Example 1

[0108] (1) Weigh out 90 parts of silicon nitride powder, 6 parts of aluminum oxide, 4 parts of yttrium oxide and 150 parts of anhydrous ethanol according to the weight, and set aside.

[0109] (2) Add silicon nitride powder, alumina and yttrium oxide from step (1) to anhydrous ethanol to obtain silicon nitride slurry; then add silicon nitride slurry to ball milling jar, add grinding balls at a ball-to-material mass ratio of 3:1, and ball mill for 2 hours at a speed of 300 r / min to obtain ball milling material.

[0110] (3) Place the ball mill material in a drying oven and dry it at a temperature of 60℃ for 8 hours to obtain dried material; then crush the dried material through a 200-mesh sieve to obtain the material to be burned.

[0111] (4) Add the material to be fired into the molding mold and dry press it at a pressure of 1.5 MPa for 1.5 min to obtain a blank; then use a cold isostatic press to further compress and densify the blank at a pressure of 200 MPa for 5 min to obtain a green blank to be fired.

[0112] (5) The green blank to be fired is placed in a boron nitride crucible, and boron nitride and silicon nitride composite powder is buried and then subjected to gas pressure sintering. The sintering pressure is 4 MPa, the sintering temperature is 1800℃, the holding time is 8h, and then the blank is cooled with the furnace to obtain silicon nitride ceramic.

[0113] The silicon nitride ceramic prepared in Comparative Example 1 was black in color and had a density of 3.22 g / cm³. 3 The phase composition is β-silicon nitride, the hardness is 15.4 GPa, and the fracture toughness is 5.6 MPa·m. 1 / 2 . Figure 5 The image shows the reflectance curve of the silicon nitride ceramic prepared in Comparative Example 1 and the color of the silicon nitride ceramic sample.

[0114] As can be seen from the preparation results of the examples and comparative examples, the silicon nitride ceramics prepared by using the components of the present invention as raw materials in Examples 1-8 are white and have good mechanical properties. This indicates that the method of the present invention can prepare white silicon nitride ceramics with high strength and good comprehensive performance.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing white silicon nitride ceramics, characterized in that, include: (1) Provide raw materials, the raw materials comprising 70-95 parts by weight of silicon nitride powder; 5-30 parts by weight of sintering aid and rare earth oxide; 100-300 parts by weight of dispersant, the rare earth oxide comprising at least one of lanthanum oxide, gadolinium oxide and lutetium oxide; the sintering aid comprising at least one of aluminum oxide and magnesium oxide; the mass ratio of the sintering aid to the rare earth oxide is 1:(1-9). (2) The raw materials are mixed and then ball-milled, and then dried to obtain the material to be burned; (3) Press the material to be fired into shape to obtain a blank to be fired; (4) The green blank to be fired is sintered and cooled to obtain the white silicon nitride ceramic.

2. The method according to claim 1, characterized in that, The dispersant includes at least one of anhydrous ethanol, anhydrous methanol, anhydrous acetone, and deionized water.

3. The method according to claim 1, characterized in that, In step (4), the green blank to be sintered is embedded with powder before sintering, and the powder used for embedding includes at least one of boron nitride powder and silicon nitride powder.

4. The method according to claim 3, characterized in that, In step (4), the sintering is carried out by gas pressure sintering, with a sintering pressure of 0.1MPa-20MPa, a sintering temperature of 1700°C-2000°C, and a holding time of 0.5h-12h.

5. The method according to claim 3, characterized in that, In step (4), the cooling rate is 0.5°C / min-20°C / min.

6. The method according to claim 3, characterized in that, The porosity of the white silicon nitride ceramic is 0.2%-5%.

7. The method according to claim 1, characterized in that, In step (2), the ball-to-material mass ratio of the ball mill is (3-4):1, the rotation speed is 200r / min-400r / min, and the ball milling time is 1h-24h.

8. The method according to claim 7, characterized in that, In step (2), the drying temperature is 50°C-80°C and the drying time is 8h-24h.

9. The method according to claim 7, characterized in that, In step (2), the material to be burned is sieved, and the mesh size of the sieve is 50-200 mesh.

10. The method according to claim 1, characterized in that, In step (3), the pressing process includes: The material to be fired is dry-pressed to obtain a blank. The dry-pressing pressure is 0.1MPa-10MPa and the time is 0.5min-10min. The billet is then subjected to cold isostatic pressing at a pressure of 100MPa-300MPa for 0.5min-10min to obtain a raw billet to be fired.

11. A white silicon nitride ceramic, characterized in that, It is prepared by the method according to any one of claims 1-10.

12. The application of the white silicon nitride ceramic of claim 11 in the medical field.

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